Androgynoceras latacosta Ammonite - Dorset Jurassic Coast (no. 19 )

These creatures first appeared 415 Million years ago in the form of a small, straight shelled creature, known as Bacrites, they quickly evolved into a variety of shapes and sizes.

Ammonites were a predatory squid-like creature with a beak-like jaw, living in shallow waters, members of an extinct group of marine Cephalopods (subclass Ammonoidea), these creatures had a ribbed chambered shell which was either spiral, part spiral or straight. They lived on every continent with sizes ranging from 1mm to 2 meters in size, living about 2 years with a few exceptions of very large Ammonites living longer, the growth rate was very rapid with females growing up to 400% bigger than the males. Home was at the open end of their shell and they secreted chambers up behind themselves about one every 4 weeks (13 a year). Ammonites moved through the water by jet propulsion, expelling water through a funnel-like opening to propel themselves in the opposite direction.

During their evolution, the ammonites faced three catastrophic events, that would eventually lead to their extinction. The first event approximately 250 Million years ago, with 9/10 surviving this event, these recovered to flourish in great numbers. Second event approximately 206 Million years ago only one species of Ammonite survived, but once again different species evolved to flourish. The third event 65 Million years ago, they became extinct along with many other creatures including the dinosaurs.

Living relatives alive today would be Octopus, Squid, Cuttlefish, Nautilus.

415 Million Years - Devonian period / 250 Million years - Permian period / 206 Million years - Late Triassic period

Ammonites found in certain types of clay are fossilises with a pearly lustre.